1. Field of the Invention
The present invention relates to a digital-to-analog (D/A) converter, and more particularly, to the improvement of the fluctuation of an output current of a current output type D/A converter.
2. Description of the Related Art
A current output type D/A converter has the following advantages:
output impedance can be reduced; PA1 high speed operation is possible; PA1 high precision resistors are unnecessary; PA1 the converter is easily incorporated into an integrated circuit (IC); and PA1 a high speed clock signal is unnecessary.
A prior art D/A converter of this kind (see JP-A-61-95623) is constructed by a logic circuit, a reference current source, and a digital-to-analog conversion section connected between the logic circuit and the reference current source. In this case, bipolar transistors of the digital-to-analog conversion section form current mirror circuits with a bipolar transistor of the reference current source. This will be explained later in detail.
In the above-mentioned prior art D/A converter, however, a resistance by switching means is introduced into each of the current mirror circuits, so that the output current is fluctuated. On the other hand, in order to minimize the above mentioned resistances and the fluctuation thereof, transistors used as the switching means can be large in size, which, however, decreases the integration.